One potato genome unravelled, three to go

The trusty spud could use some genetic improvement, especially in resisting disease. But the humble tuber is a genetic jungle: most potatoes hold four copies of its genome, each very different from the others, making sequencing a nightmare.

A massive collaboration among scientists on four continents has now solved the problem by growing a whole plant in culture from one pollen cell. This produced potatoes with just one copy of the genome, which the researchers were able to sequence. The "monoploid" sequence provided a template they could then use to piece together the DNA sequences of a rare potato variety which is diploid, meaning it carries two genomes.

Even so, the team could find only enough matches to piece together 55 per cent of the diploid's sequence. "We have to wait now for better sequencing technology before we can tackle potatoes with four genomes," says Robin Buell of Michigan State University in East Lansing, a lead researcher. New technology that sequences longer fragments of a DNA molecule at a time, now under development, will be needed to sequence normal spuds.

Just the amount of sequencing published this week, however, has already revealed why potato diseases are a problem, says Buell: a lot of the genes thought to confer resistance to pathogens are mutated and broken.

The sequence should also make breeding better potatoes quicker and easier. It will be used to guide gene surveys of commercial breeding lines and find sequences associated with desired traits such as disease resistance – or better frying or mashing qualities. That will allow breeders to screen experimental crosses of breeding potatoes for the requisite DNA and find out which hybrids have the required traits quickly and easily, without having to grow many plants to maturity.

Journal reference: Nature, DOI: 10.1038/nature10158

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Getting a grip, one genome at a time (Image: Jason Alden/Rex Features)